Macrobrachium malcolmsonii, M. nobilii, and M. lamarrei were used to investigate their preferences among three substrate colors (dark brown, black, and light brown), shelter type (black tile and black PVC pipe), color (black and brown tile), and diameter, and regarding intraand inter-species habitation. Both M. lamarrei and M. malcolmsonii preferred dark-brown substrate, while M. nobilii preferred black. The choice of shelter type was monitored by time spent by each species in a black PVC tube or in a black tile. Within a 24-h period, M. malcolmsonii spent a greater amount of time (60.5%) within the black tile, while M. nobilii spent more time (71%) inside the black PVC tube. M. lamarrei always occupied an open area and thus was discarded from further experiments. If we consider daytime and nighttime separately, both species spent more time within the black tile during the day than during the night. Choice of shelter color was tested with black and brown shelters of identical size; both species exclusively preferred the black. Between the species, despite the smaller body size both male and female M. nobilii succeeded in evicting M. malcolmsonii, suggesting a stronger shelter affinity. When competing for shelter within the same species, a male was more dominant than a conspecific female and juvenile. Similarly males of both species allowed conspecific juveniles to cohabit for about 16% of the time. Male M. malcolmsonii also allowed cohabitation of a female for 31.2% of the time, unlike the male M. nobilii, which did not allow female cohabitation at all. Both species preferred shelters that were adjusted to their meral spread as opposed to their carapace width. The possibility of taking meral spread as a taxonomic character was also indicated. The study also found a linear relationship between exuvium weight and shelter affinity among the three species. A lower ratio indicated a higher shelter affinity. The exuvium/total body weight ratio confirmed the shelter affinity, which was ranked as M. nobilii (0.275) < M. malcolmsonii (0.312) < M. lamarrei (0.426).

River Cauvery, one of the perennial rivers of southern India, originates in Talakaveri, Brahmagiri Hills (12°25'N & 75°34'E) of the Western Ghats, in Coorg District of Karnataka and flows eastwards through Tamil Nadu into Bay of Bengal Sea. It runs a distance of 1171km with many contributories and tributaries. The major reservoir of river Cauvery in Tamil Nadu is Mettur Dam, where from water is usually released for irrigation from July to January. Due to minimum water flow from March to June the river bed between the river Anicut to the tail end zone gradually dries up leading to mass mortality of Macrobrachium species (Mariappan & Balasundaram, 1999).In this study, the freshwater prawn distribution in river Cauvery was studied from Mettur, Jedarpalayam, Grand Anicut and Lower Anicut, and Muthupettai in river Koraiyaru, a tributary of Cauvery. Among these, Lower Anicut is the main collection center for juveniles of Macrobrachium malcolmsonii, where the Tamil Nadu State Fisheries Department has the sole authority for the collection and sale of prawn seeds during monsoon. Farmers from the entire state come here to purchase juveniles for prawn farming from October to January.

Fatty acid profiles of midgut gland (MG), ovary and eggs of Macrobrachium rosenbergii of wild and farm reared brooders indicate a significant variation of their components during the sexual maturation and spawning. In both groups, major fatty acids found in the chosen tissues were 14:0, 16:0, 18:0, 18:1n-9, 18:2n-6, 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3. Of these, saturated fatty acids dominate over the monounsaturated (MUFA), polyunsaturated (PUFA) and highly unsaturated fatty acids (HUFA). Though all the four groups of fatty acids are found in both groups except n-3 HUFA (P>0.05) other categories are found in higher wild brooders (P<0.05). There was a significant difference in total weight, total length and clutch weight (P<0.05) between farm and wild brooders, but the gonadosomatic index (GSI) and midgut gland somatic index (MSI) did not vary significantly (P>0.05).

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